Roller bearing with means for giving the rollers a positive skew angle

ABSTRACT

A roller bearing of the type incorporating an outer and an inner race ring (1, 3) having confronting race tracks (2, 4), with lands (A, B) situated axially outside said race tracks and a number of rollers (5) being interposed between and in contact with said race tracks, said rollers (5) and race tracks (2, 4) having longitudinal section profiles of a radious of curvature, which is bigger than the distance between the outer race track and the axis of the bearing, as measured perpendicularly to the race track, which rollers (5) thereby are axially movable along the race tracks without being hindred by axial limitations at the race tracks, in order to allow relative misalignment and axial displaceability of the race tracks, wherein at least portions of the areas (A, B, G, J) of the race rings axially outside the zone (H) subjected to bearing load, have such surface finish and/or profile as to contribute in giving the rollers (5) a positive skew angle.

The present invention relates to a roller bearing of the typeincorporating an outer and an inner race ring having confronting racetracks and a number of rollers being interposed between and in contactwith said race tracks, said rollers and race tracks having longitudinalsection profiles of a radius of curvature which is bigger than thedistance between the outer race track and the axis of the bearing, asmeasured perpendicularly to the race track, which rollers thereby areaxially movable across the race tracks without being hindred by axiallimitations at the race tracks, in order to allow relative misalignmentand axial displaceability of the race tracks and it refers to such aroller bearing having means for giving the rollers a positive skewangle, when axially displaced.

Bearing of this type are known e.g. from EP-B1-0175858 andEP-B1-0520968, and they combine different advantages from other types ofbearings, such as axial mobility as a cylindrical roller bearing, selfalignment as a spherical roller bearing and low section height as aneedle roller bearing.

The present type of bearing has the ability of allowing axialdisplacement between the rollers and the race rings and also between thetwo race rings, and it also permits high degrees of misalignment. Whenthe rings of such a bearing are displaced axially, the contact angleresulting therefrom is small. Particularly when the internal clearanceof the bearing is small, or when the bearing is pre-loaded, it isessential that the skew rolling angle, if any, is positive or zero, asotherwise there can be a tendency that the race rings are pulled in overeach other, thereby risking that the rollers are being jammed betweenthe race tracks, if the axial guidance of the shaft from other bearingsis poor or absent.

The skew angle is defined as positive when the axial friction forcesfrom the roller on the race ways arising as a result of roller skew,have the same axial direction as the axial component of the normal loadfrom the roller on the raceway.

A positive skew angle gives the bearing capability of taking up morethrust, whereas a negative skew angle reduces this capability and evenmight damage the bearing. In rolling bearings it is often desirable tocontrol that the bearing has a positive skew angle in order to ascertainthat the friction forces emanating from the contact between the rollerand its adjoining race tracks cooperate with the friction forces atnormal rolling for giving the rolling bodies a minimum of friction underload, and this is often achieved by giving the race track surfaces,i.e., the surfaces of the race rings against which the roller normallyrolls, certain surface patterns.

In a bearing of the type now concerned, it however is possible to obtainroller skew control, e.g. for avoiding the above mentioned tendenciesthat the race rings are pulled in over each other, also in othermanners, and this is achieved in accordance with the characterizingpart.

BRIEF DESCRIPTION OF THE FIGURES

Hereinafter the invention will be further described by way of anembodiment schematically shown in the accompanying drawing.

FIG. 1 shows a section through a roller bearing of the type concerned ina neutral position,

FIG. 2 is a view corresponding to FIG. 1, but with the bearing rings andthe rollers in axially displaced positions.

FIG. 1 of the drawing shows a section through a portion (half) of abearing of the type referred to and incorporating an outer race ring 1having at its inner envelope surface a first race track 2, and an innerrace ring 3, having at its outer envelope surface a second race track 4.These two race tracks 2, 4 define between them an annular space occupiedby a number of rollers 5. The race rings 1, 3 are shown in crosssection, although they are not hatched in order to increase theclearness of the presentation.

The rollers 5 and the race tracks 2, 4 of the bearing of this type haveessentially the same radius of curvature R, and this radius of curvatureis bigger than the geometrical radius of the bearing itself.

The rollers 5 in such a bearing contact the outer race track 2, theinner race track 4 and in the case the bearing has a roller cage (notshown in the drawing), which keeps the rollers spaced apart in thecircumferential direction, also this cage. In operation, the rollers 5normally assume a certain angle relative to the direction of rolling,resulting in both rolling and axial sliding motion and this angle istermed the skew angle, defined as the angle between the axis of rotationof the roller and a plane normal to the path of relative motion of theraceways confronting the rollers.

In FIG. 1 the bearing is shown with the race rings 1 and 3 and therollers 5 in neutral positions, i.e. the race rings are neitherangularly nor axially displaced relative to each other and the rollersare positioned centrally and having the roller axis at leastsubstantially parallel to the bearing axis. In this position the rollerscontact only the race tracks 2 and 4 resp. of the race rings, whereasthe lands positioned on both sides axially outside the race tracks 2 and4, and in the drawing marked A and B resp., are unoccupied by therollers 5.

FIG. 2 shows in a view corresponding to FIG. 1, the bearing i.a.subjected to an axial load F, (and a similar counterload F') under whichload the race rings 1 and 3 and the rollers 5 are axially displacedrelative to each other. For simplicity we now will put the viewer in thecoordinate system of the roller. The outer race ring 1 then rotates in arelative direction as compared to the inner race ring 3 shown with apointed circle in FIG. 2, representing a motion against the viewer,whereas the inner race ring 3 rotates in a direction away from theviewer as shown with a crossed circle. Under these conditions andsubjected to the axial load F, the roller 5 will have a pure rollingcontact with each race track 2 and 4 resp. only in two points, intimatedas C and D, whereas the roller in other positions along its axialextension will be subjected both to rolling and sliding motion,resulting in peripheral sliding influences on the roller as shown withthe same type of direction markings as on the race rings.

For reducing the tendencies for the rollers 5 from taking up negativeskew angles under such conditions it now is suggested to utilize theareas axially outside the zone H, wherein the rollers are normallysubjected to load. Each one of these areas consists of a land A or Bresp. and a portion G outside said load zone H, wherein the rollersnormally will be unloaded, for providing the bearing of this type withmeans ascertaining that the rollers will be subjected to forces whichtend to give the roller a positive skew angle. This can be obtained inthat the contacts between the unloaded areas G and/or the lands A, B andthe rollers 5 are designed in such a manner as to give as low frictionalforces as possible.

This can be achieved either by giving the unloaded areas G, and/or thelands such high surface finish as possible resulting in a very lowcoefficient of friction at contact with the these regions, or by makingthe land with a modified profile portion, i.e. an extension notcontinuously following the extension of the race track profile, butbeing somewhat outwardly offset in radial direction from this as seen ina direction away from the roller centre, such as intimated at E at theland A in FIG. 2. Such effect can also be obtained with other knownmodifications of the surface topography of the lands. Anotherpossibility is to provide at least one outer portion of said areas witha recess, such as intimated at J.

The invention is not limited to the embodiment shown and described butcan be varied and modified within the scope of the accompanying claims,and although the bearing has been shown as a cage-less bearing it isevident that roller skew guidance can be achieved in the same manneralso with a bearing with the rollers guided in a cage. Although notspecifically mentioned or shown it also is evident that the means forascertaining positive roller skew angle can be provided on one or bothrace rings.

What is claimed is:
 1. Roller bearing comprising an outer and an innerrace ring having confronting outer and inner race tracks respectivelywith lands situated axially outside said outer and inner race tracks anda number of rollers provided between and in contact with said outer andinner race tracks, the rollers and outer and inner race tracks havinglongitudinal section profiles with a radius of curvature, which isbigger than a distance between the outer race track and an axis of thebearing, measured perpendicularly to the outer race track, the rollersbeing axially movable along the outer and inner race tracks withoutbeing hindred by axial confinements at the outer and inner race tracksfor the purpose of permitting relative misalignment and axialdisplaceability for the outer and inner race tracks, at least portionsof areas in the inner and outer race rings, in non-displaced positionsituated axially outside a zone, which is subjected to bearing load,having a surface finish and/or profile that contributes in giving therollers a positive skew angle, and which is achieved by either thatthese areas are surfaces having reduced friction in form of smoothsurfaces, that these surfaces have modified profile portions whichreduce contact pressure between these areas and the rollers atconditions of mutual displacement between the race rings in the axialdirection, and that said areas have at least one recessed portion. 2.Roller bearing as claimed in claim 1, said areas on the race rings arethe lands situated axially outside the race tracks.